Iejimalides A and B inhibit lysosomal vacuolar H+-ATPase (V-ATPase) activity and induce S-phase arrest and apoptosis in MCF-7 cells

Calpains, the proteases of two faces controlling the epithelial homeostasis in mammary gland

Calpain-1 and calpain-2 are calcium-dependent Cys-proteases ubiquitously expressed in mammalian tissues with a processive, rather than degradative activity. They are crucial for physiological mammary gland homeostasis as well as for breast cancer progression. A growing number of evidences indicate that their pleiotropic functions depend on the cell type, tissue and biological context where they are expressed or dysregulated. This review considers these standpoints to cover the paradoxical role of calpain-1 and -2 in the mammary tissue either, under the physiological conditions of the postlactational mammary gland regression or the pathological context of breast cancer. The role of both calpains will be examined and discussed in both conditions, followed by a brief snapshot on the present and future challenges for calpains, the two-gateway proteases towards tissue homeostasis or tumor development.

Loss of vacuolar-type H+-ATPase induces caspase-independent necrosis-like death of hair cells in zebrafish neuromasts

The vacuolar-type H+-ATPase (V-ATPase) is a multi-subunit proton pump that regulates cellular pH. V-ATPase activity modulates several cellular processes, but cell-type-specific functions remain poorly understood. Patients with mutations in specific V-ATPase subunits can develop sensorineural deafness, but the underlying mechanisms are unclear. Here, we show that V-ATPase mutations disrupt the formation of zebrafish neuromasts, which serve as a model to investigate hearing loss. V-ATPase mutant neuromasts are small and contain pyknotic nuclei that denote dying cells. Molecular markers and live imaging show that loss of V-ATPase induces mechanosensory hair cells in neuromasts, but not neighboring support cells, to undergo caspase-independent necrosis-like cell death. This is the first demonstration that loss of V-ATPase can lead to necrosis-like cell death in a specific cell type in vivo. Mechanistically, loss of V-ATPase reduces mitochondrial membrane potential in hair cells. Modulating the mitochondrial permeability transition pore, which regulates mitochondrial membrane potential, improves hair cell survival. These results have implications for understanding the causes of sensorineural deafness, and more broadly, reveal functions for V-ATPase in promoting survival of a specific cell type in vivo.

Membrane Transport Proteins in Osteoclasts: The Ins and Outs

During bone resorption, the osteoclast must sustain an extraordinarily low pH environment, withstand immense ionic pressures, and coordinate nutrient and waste exchange across its membrane to sustain its unique structural and functional polarity. To achieve this, osteoclasts are equipped with an elaborate set of membrane transport proteins (pumps, transporters and channels) that serve as molecular ‘gatekeepers’ to regulate the bilateral exchange of ions, amino acids, metabolites and macromolecules across the ruffled border and basolateral domains. Whereas the importance of the vacuolar-ATPase proton pump and chloride voltage-gated channel 7 in osteoclasts has long been established, comparatively little is known about the contributions of other membrane transport proteins, including those categorized as secondary active transporters. In this Special Issue review, we provide a contemporary update on the ‘ins and outs’ of membrane transport proteins implicated in osteoclast differentiation, function and bone homeostasis and discuss their therapeutic potential for the treatment of metabolic bone diseases.

Bioactive compounds from marine invertebrates as potent anticancer drugs: the possible pharmacophores modulating cell death pathways

Marine invertebrates are extremely diverse, largely productive, untapped oceanic resources with chemically unique bioactive lead compound contributing a wide range of screening for the discovery of anticancer compounds. The lead compounds have unfurled an extensive array of pharmacological properties owing to the presence of polyphenols, alkaloids, terpenoids and other secondary metabolites. The antioxidant, immunomodulatory and anti-tumor activities exhibited, are possibly regulated by the apoptosis induction, scavenging of ROS and modulation of cellular signaling pathways to defy the cellular deafness during carcinogenesis. Despite the enriched bioactive compounds, the marine invertebrates are largely unexplored as identification, screening, pre-clinical and clinical assessment of lead compounds and their synthetic analogs remain a major task to be solved. In the current review, we focus on the principle strategy and underlying mechanisms deployed by the bioactive anticancer compounds derived from marine invertebrates to combat cancer with special insight into the cell death mechanism.

Biological Effects of a Simplified Synthetic Analogue of Ion-Channel-Forming Polytheonamide B on Plasma Membrane and Lysosomes

Polytheonamide B (1) is a linear 48-mer natural peptide with alternating d- and l-amino acid residues. Compound 1 forms conducting channels for monovalent ions and exhibits potent cytotoxicity against MCF-7 cells. Previously, we reported that nanomolar concentrations of 1 induce plasma membrane depolarization and lysosomal pH disruption, which triggers apoptosis. Here, we report the cellular localization and biological action of a simplified synthetic analogue of 1, polytheonamide mimic 3. Compared with 1, the toxicity of 3 against MCF-7 cells is 16 times weaker. Although its plasma membrane depolarization effect is only 3.6 times lower, more 3 (20-fold) is required to neutralize lysosomal pH. Thus, the effective concentrations for lysosomal neutralization and cytotoxicity by 3 are comparable. These results strongly suggest that the activity of 3 against the lysosomal membrane is more important for apoptotic cell death than its effects on the plasma membrane, and provide valuable information regarding the unique behavior of polytheonamide-based molecules.

Differential regulation of AMP-activated protein kinase in healthy and cancer cells explains why V-ATPase inhibition selectively kills cancer cells

The cellular energy sensor AMP-activated protein kinase (AMPK) is a metabolic hub regulating various pathways involved in tumor metabolism. Here we report that vacuolar H⁺-ATPase (V-ATPase) inhibition differentially affects regulation of AMPK in tumor and nontumor cells and that this differential regulation contributes to the selectivity of V-ATPase inhibitors for tumor cells. In nonmalignant cells, the V-ATPase inhibitor archazolid increased phosphorylation and lysosomal localization of AMPK. We noted that AMPK localization has a prosurvival role, as AMPK silencing decreased cellular growth rates. In contrast, in cancer cells, we found that AMPK is constitutively active and that archazolid does not affect its phosphorylation and localization. Moreover, V-ATPase-independent AMPK induction in tumor cells protected them from archazolid-induced cytotoxicity, further underlining the role of AMPK as a prosurvival mediator. These observations indicate that AMPK regulation is uncoupled from V-ATPase activity in cancer cells and that this makes them more susceptible to cell death induction by V-ATPase inhibitors. In both tumor and healthy cells, V-ATPase inhibition induced a distinct metabolic regulatory cascade downstream of AMPK, affecting ATP and NADPH levels, glucose uptake, and reactive oxygen species production. We could attribute the prosurvival effects to AMPK's ability to maintain redox homeostasis by inhibiting reactive oxygen species production and maintaining NADPH levels. In summary, the results of our work indicate that V-ATPase inhibition has differential effects on AMPK-mediated metabolic regulation in cancer and healthy cells and explain the tumor-specific cytotoxicity of V-ATPase inhibition.

Connecting lysosomes and mitochondria - a novel role for lipid metabolism in cancer cell death

Background

The understanding of lysosomes has been expanded in recent research way beyond their view as cellular trash can. Lysosomes are pivotal in regulating metabolism, endocytosis and autophagy and are implicated in cancer. Recently it was discovered that the lysosomal V-ATPase, which is known to induce apoptosis, interferes with lipid metabolism in cancer, yet the interplay between these organelles is poorly understood.

Methods

LC-MS/MS analysis was performed to investigate lipid distribution in cells. Cell survival and signaling pathways were analyzed by means of cell biological methods (qPCR, Western Blot, flow cytometry, CellTiter-Blue). Mitochondrial structure was analyzed by confocal imaging and electron microscopy, their function was determined by flow cytometry and seahorse measurements.

Results

Our data reveal that interfering with lysosomal function changes composition and subcellular localization of triacylglycerids accompanied by an upregulation of PGC1α and PPARα expression, master regulators of energy and lipid metabolism. Furthermore, cardiolipin content is reduced driving mitochondria into fission, accompanied by a loss of membrane potential and reduction in oxidative capacity, which leads to a deregulation in cellular ROS and induction of mitochondria-driven apoptosis. Additionally, cells undergo a metabolic shift to glutamine dependency, correlated with the fission phenotype and sensitivity to lysosomal inhibition, most prominent in Ras mutated cells.

Conclusion

This study sheds mechanistic light on a largely uninvestigated triangle between lysosomes, lipid metabolism and mitochondrial function. Insight into this organelle crosstalk increases our understanding of mitochondria-driven cell death. Our findings furthermore provide a first hint on a connection of Ras pathway mutations and sensitivity towards lysosomal inhibitors.

Graphical Abstract

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0399-2) contains supplementary material, which is available to authorized users.

V-ATPases and osteoclasts: ambiguous future of V-ATPases inhibitors in osteoporosis

Vacuolar ATPases (V-ATPases) play a critical role in regulating extracellular acidification of osteoclasts and bone resorption. The deficiencies of subunit a3 and d2 of V-ATPases result in increased bone density in humans and mice. One of the traditional drug design strategies in treating osteoporosis is the use of subunit a3 inhibitor. Recent findings connect subunits H and G1 with decreased bone density. Given the controversial effects of ATPase subunits on bone density, there is a critical need to review the subunits of V-ATPase in osteoclasts and their functions in regulating osteoclasts and bone remodeling. In this review, we comprehensively address the following areas: information about all V-ATPase subunits and their isoforms; summary of V-ATPase subunits associated with human genetic diseases; V-ATPase subunits and osteopetrosis/osteoporosis; screening of all V-ATPase subunits variants in GEFOS data and in-house data; spectrum of V-ATPase subunits during osteoclastogenesis; direct and indirect roles of subunits of V-ATPases in osteoclasts; V-ATPase-associated signaling pathways in osteoclasts; interactions among V-ATPase subunits in osteoclasts; osteoclast-specific V-ATPase inhibitors; perspective of future inhibitors or activators targeting V-ATPase subunits in the treatment of osteoporosis.

Solid-Phase Total Synthesis and Dual Mechanism of Action of the Channel-Forming 48-mer Peptide Polytheonamide B

Polytheonamide B (1) is a unique peptide natural product because of its extremely complex structure, a channel-forming ability in vitro, and the extremely potent cytotoxicity. The 48-mer sequence of 1 comprises alternating d,l-amino acids and possesses an array of sterically bulky β-tetrasubstituted and hydrogen bond forming residues. These unusual structural features are believed to drive 1 to fold into a 4.5 nm long tube, form a transmembrane ion channel at the plasma membrane, and exert cytotoxicity. Despite its potential biological application, however, multiple substitutions by these unusual residues significantly heightened the synthetic challenges, impeding the solid-phase peptide synthesis (SPPS) of 1. In this study, we first addressed the synthesis problem by extensive optimization of various factors of the SPPS. Adaptation of a new protective group strategy allowed for elongation of a 37-mer peptide on resin, to which an N-terminal 11-mer fragment was condensed. Removal of the 18 protective groups and resin gave rise to 1 in excellent overall yield (4.5%, 76 steps from 17). The SPPS protocol is operationally simple and was proven easily amenable to total synthesis of the fluorescent 48-mer probe 2. Synthetic 1 and 2 were utilized for analysis of their cellular behavior. Reflecting its ion-channel function, the addition of 1 to MCF-7 cells rapidly diminished a potential across the plasma membrane. Furthermore, fluorescence imaging study revealed that 1 and 2 were also internalized into the cells, accumulating in acidic lysosomes and neutralizing the lysosomal pH gradient. These new findings indicated that 1 is capable of exerting two functions upon causing apoptotic cell death of mammalian cells: It induces free cation transport across the plasma as well as lysosomal membranes. The present chemical and biological studies provide valuable information for the design and synthesis of polytheonamide-based molecules with more potent and selective biological activities.

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

Vacuolar ATPase (V-ATPase) is an ATP-dependent H+ -transporter that pumps protons across intracellular and plasma membranes. It consists of a large multi-subunit protein complex and influences a wide range of cellular processes. This review focuses on emerging evidence for the roles for V-ATPase in cancer. This includes how V-ATPase dysregulation contributes to cancer growth, metastasis, invasion and proliferation, and the potential link between V-ATPase and the development of drug resistance.

V-ATPase-dependent repression of androgen receptor in prostate cancer cells

Prostate Cancer (PCa) is the most commonly diagnosed cancer and the third leading cause of death for men in the United States. Suppression of androgen receptor (AR) expression is a desirable mechanism to manage PCa. Our studies showed that AR expression was reduced in LAPC4 and LNCaP PCa cell lines treated with nanomolar concentrations of the V-ATPase inhibitor concanamycin A (CCA). This treatment decreased PSA mRNA levels, indicative of reduced AR activity. V-ATPase-dependent repression of AR expression was linked to defective endo-lysosomal pH regulation and reduced AR expression at the transcriptional level. CCA treatment increased the protein level and nuclear localization of the alpha subunit of the transcription factor HIF-1 (HIF-1α) in PCa cells via decreased hydroxylation and degradation of HIF-1α. The addition of iron (III) citrate restored HIF-1α hydroxylation and decreased total HIF-1α levels in PCa cells treated with CCA. Moreover, iron treatment partially rescued CCA-mediated AR repression. Dimethyloxalylglycine (DMOG), which prevents HIF-1α degradation independently of V-ATPase, also decreased AR levels, supporting our hypothesis that HIF-1α serves as a downstream mediator in the V-ATPase-AR axis. We propose a new V-ATPase-dependent mechanism to inhibit androgen receptor expression in prostate cancer cells involving defective endosomal trafficking of iron and the inhibition of HIF-1 α-subunit turnover.

The a3 isoform of subunit a of the vacuolar ATPase localizes to the plasma membrane of invasive breast tumor cells and is overexpressed in human breast cancer

The vacuolar (H+)-ATPases (V-ATPases) are a family of ATP-driven proton pumps that acidify intracellular compartments and transport protons across the plasma membrane. Previous work has demonstrated that plasma membrane V-ATPases are important for breast cancer invasion in vitro and that the V-ATPase subunit a isoform a3 is upregulated in and critical for MDA-MB231 and MCF10CA1a breast cancer cell invasion. It has been proposed that subunit a3 is present on the plasma membrane of invasive breast cancer cells and is overexpressed in human breast cancer. To test this, we used an a3-specific antibody to assess localization in breast cancer cells. Subunit a3 localizes to the leading edge of migrating breast cancer cells, but not the plasma membrane of normal breast epithelial cells. Furthermore, invasive breast cancer cells express a3 throughout all intracellular compartments tested, including endosomes, the Golgi, and lysosomes. Moreover, subunit a3 knockdown in MB231 breast cancer cells reduces in vitro migration. This reduction is not enhanced upon addition of a V-ATPase inhibitor, suggesting that a3-containing V-ATPases are critical for breast cancer migration. Finally, we have tested a3 expression in human breast cancer tissue and mRNA prepared from normal and cancerous breast tissue. a3 mRNA was upregulated 2.5-47 fold in all breast tumor cDNA samples tested relative to normal tissue, with expression generally correlated to cancer stage. Furthermore, a3 protein expression was increased in invasive breast cancer tissue relative to noninvasive cancer and normal breast tissue. These studies suggest that subunit a3 plays an important role in invasive human breast cancer.

F-actin reorganization by V-ATPase inhibition in prostate cancer

The vacuolar ATPase (V-ATPase) proton pump sustains cellular pH homeostasis, and its inhibition triggers numerous stress responses. However, the cellular mechanisms involved remain largely elusive in cancer cells. We studied V-ATPase in the prostate cancer (PCa) cell line PC-3, which has characteristics of highly metastatic PCa. V-ATPase inhibitors impaired endo-lysosomal pH, vesicle trafficking, migration, and invasion. V-ATPase accrual in the Golgi and recycling endosomes suggests that traffic of internalized membrane vesicles back to the plasma membrane was particularly impaired. Directed movement provoked co-localization of V-ATPase containing vesicles with F-actin near the leading edge of migrating cells. V-ATPase inhibition prompted prominent F-actin cytoskeleton reorganization. Filopodial projections were reduced, which related to reduced migration velocity. F-actin formed novel cytoplasmic rings. F-actin rings increased with extended exposure to sublethal concentrations of V-ATPase inhibitors, from 24 to 48 h, as the amount of alkalinized endo-lysosomal vesicles increased. Studies with chloroquine indicated that F-actin rings formation was pH-dependent. We hypothesize that these novel F-actin rings assemble to overcome widespread traffic defects caused by V-ATPase inhibition, similar to F-actin rings on the surface of exocytic organelles.

Summary: V-ATPase activates multiple stress responses. In prostate cancer, sub-lethal concentrations of V-ATPase inhibitors trigger widespread traffic defects. F-actin assembles into rings that mimic those seen during regulated exocytosis.

The interaction of the bioinsecticide PA1b (Pea Albumin 1 subunit b) with the insect V-ATPase triggers apoptosis

PA1b (Pea Albumin 1, subunit b) peptide is an entomotoxin, extracted from Legume seeds, with a lethal activity towards several insect pests, such as mosquitoes, some aphids and cereal weevils. This toxin acts by binding to the subunits c and e of the plasma membrane H+-ATPase (V-ATPase) in the insect midgut. In this study, two cereal weevils, the sensitive Sitophilus oryzae strain WAA42, the resistance Sitophilus oryzae strain ISOR3 and the insensitive red flour beetle Tribolium castaneum, were used in biochemical and histological experiments to demonstrate that a PA1b/V-ATPase interaction triggers the apoptosis mechanism, resulting in insect death. Upon intoxication with PA1b, apoptotic bodies are formed in the cells of the insect midgut. In addition, caspase-3 enzyme activity occurs in the midgut of sensitive weevils after intoxication with active PA1b, but not in the midgut of resistant weevils. These biochemical data were confirmed by immuno-histochemical detection of the caspase-3 active form in the midgut of sensitive weevils. Immuno-labelling experiments also revealed that the caspase-3 active form and V-ATPase are close-localized in the insect midgut. The results concerning this unique peptidic V-ATPase inhibitor pave the way for the utilization of PA1b as a promising, more selective and eco-friendly insecticide.

The Function of V-ATPases in Cancer

The vacuolar ATPases (V-ATPases) are a family of proton pumps that couple ATP hydrolysis to proton transport into intracellular compartments and across the plasma membrane. They function in a wide array of normal cellular processes, including membrane traffic, protein processing and degradation, and the coupled transport of small molecules, as well as such physiological processes as urinary acidification and bone resorption. The V-ATPases have also been implicated in a number of disease processes, including viral infection, renal disease, and bone resorption defects. This review is focused on the growing evidence for the important role of V-ATPases in cancer. This includes functions in cellular signaling (particularly Wnt, Notch, and mTOR signaling), cancer cell survival in the highly acidic environment of tumors, aiding the development of drug resistance, as well as crucial roles in tumor cell invasion, migration, and metastasis. Of greatest excitement is evidence that at least some tumors express isoforms of V-ATPase subunits whose disruption is not lethal, leading to the possibility of developing anti-cancer therapeutics that selectively target V-ATPases that function in cancer cells.

(Pro)renin receptor (ATP6AP2) depletion arrests As4.1 cells in the G0/G1 phase thereby increasing formation of primary cilia

The (pro)renin receptor [(P)RR, ATP6AP2] is a multifunctional transmembrane protein that activates local renin-angiotensin systems, but also interacts with Wnt pathways and vacuolar H⁺ -ATPase (V-ATPase) during organogenesis. The aim of this study was to characterize the role of ATP6AP2 in the cell cycle in more detail. ATP6AP2 down-regulation by siRNA in renal As4.1 cells resulted in a reduction in the rate of proliferation and a G0/G1 phase cell cycle arrest. We identified a number of novel target genes downstream of ATP6AP2 knock-down that were related to the primary cilium (Bbs-1, Bbs-3, Bbs-7, Rabl5, Ttc26, Mks-11, Mks-5, Mks-2, Tctn2, Nme7) and the cell cycle (Pierce1, Clock, Ppif). Accordingly, the number of cells expressing the primary cilium was markedly increased. We found no indication that these effects were dependent of V-ATPase activity, as ATP6AP2 knock-down did not affect lysosomal pH and bafilomycin A neither influenced the ciliary expression pattern nor the percentage of ciliated cells. Furthermore, ATP6AP2 appears to be essential for mitosis. ATP6AP2 translocated from the endoplasmatic reticulum to mitotic spindle poles (pro-, meta- and anaphase) and the central spindle bundle (telophase) and ATP6AP2 knock-down results in markedly deformed spindles. We conclude that ATP6AP2 is necessary for cell division, cell cycle progression and mitosis. ATP6AP2 also inhibits ciliogenesis, thus promoting proliferation and preventing differentiation.

Recent Insights into the Structure, Regulation, and Function of the V-ATPases

The vacuolar (H(+))-ATPases (V-ATPases) are ATP-dependent proton pumps that acidify intracellular compartments and are also present at the plasma membrane. They function in such processes as membrane traffic, protein degradation, virus and toxin entry, bone resorption, pH homeostasis, and tumor cell invasion. V-ATPases are large multisubunit complexes, composed of an ATP-hydrolytic domain (V1) and a proton translocation domain (V0), and operate by a rotary mechanism. This review focuses on recent insights into their structure and mechanism, the mechanisms that regulate V-ATPase activity (particularly regulated assembly and trafficking), and the role of V-ATPases in processes such as cell signaling and cancer. These developments have highlighted the potential of V-ATPases as a therapeutic target in a variety of human diseases.

Estimating the rotation rate in the vacuolar proton-ATPase in native yeast vacuolar membranes

The rate of rotation of the rotor in the yeast vacuolar proton-ATPase (V-ATPase), relative to the stator or steady parts of the enzyme, is estimated in native vacuolar membrane vesicles from Saccharomyces cerevisiae under standardised conditions. Membrane vesicles are formed spontaneously after exposing purified yeast vacuoles to osmotic shock. The fraction of total ATPase activity originating from the V-ATPase is determined by using the potent and specific inhibitor of the enzyme, concanamycin A. Inorganic phosphate liberated from ATP in the vacuolar membrane vesicle system, during ten min of ATPase activity at 20 °C, is assayed spectrophotometrically for different concanamycin A concentrations. A fit of the quadratic binding equation, assuming a single concanamycin A binding site on a monomeric V-ATPase (our data are incompatible with models assuming multiple binding sites), to the inhibitor titration curve determines the concentration of the enzyme. Combining this with the known ATP/rotation stoichiometry of the V-ATPase and the assayed concentration of inorganic phosphate liberated by the V-ATPase, leads to an average rate of ~10 Hz for full 360° rotation (and a range of 6-32 Hz, considering the ± standard deviation of the enzyme concentration), which, from the time-dependence of the activity, extrapolates to ~14 Hz (8-48 Hz) at the beginning of the reaction. These are lower-limit estimates. To our knowledge, this is the first report of the rotation rate in a V-ATPase that is not subjected to genetic or chemical modification and is not fixed to a solid support; instead it is functioning in its native membrane environment.

Further characterization of ATP6V0A2-related autosomal recessive cutis laxa

Autosomal recessive cutis laxa (ARCL) syndromes are phenotypically overlapping, but genetically heterogeneous disorders. Mutations in the ATP6V0A2 gene were found to underlie both, autosomal recessive cutis laxa type 2 (ARCL2), Debré type, and wrinkly skin syndrome (WSS). The ATP6V0A2 gene encodes the a2 subunit of the V-type H(+)-ATPase, playing a role in proton translocation, and possibly also in membrane fusion. Here, we describe a highly variable phenotype in 13 patients with ARCL2, including the oldest affected individual described so far, who showed strikingly progressive dysmorphic features and heterotopic calcifications. In these individuals we identified 17 ATP6V0A2 mutations, 14 of which are novel. Furthermore, we demonstrate a localization of ATP6V0A2 at the Golgi-apparatus and a loss of the mutated ATP6V0A2 protein in patients' dermal fibroblasts. Investigation of brefeldin A-induced Golgi collapse in dermal fibroblasts as well as in HeLa cells deficient for ATP6V0A2 revealed a delay, which was absent in cells deficient for the ARCL-associated proteins GORAB or PYCR1. Furthermore, fibroblasts from patients with ATP6V0A2 mutations displayed elevated TGF-β signalling and increased TGF-β1 levels in the supernatant. Our current findings expand the genetic and phenotypic spectrum and suggest that, besides the known glycosylation defect, alterations in trafficking and signalling processes are potential key events in the pathogenesis of ATP6V0A2-related ARCL.

Calpains mediate epithelial-cell death during mammary gland involution: mitochondria and lysosomal destabilization

Our aim was to elucidate the physiological role of calpains (CAPN) in mammary gland involution. Both CAPN-1 and -2 were induced after weaning and its activity increased in isolated mitochondria and lysosomes. CAPN activation within the mitochondria could trigger the release of cytochrome c and other pro-apoptotic factors, whereas in lysosomes it might be essential for tissue remodeling by releasing cathepsins into the cytosol. Immunohistochemical analysis localized CAPNs mainly at the luminal side of alveoli. During weaning, CAPNs translocate to the lysosomes processing membrane proteins. To identify these substrates, lysosomal fractions were treated with recombinant CAPN and cleaved products were identified by 2D-DIGE. The subunit b(2) of the v-type H(+) ATPase is proteolyzed and so is the lysosomal-associated membrane protein 2a (LAMP2a). Both proteins are also cleaved in vivo. Furthermore, LAMP2a cleavage was confirmed in vitro by addition of CAPNs to isolated lysosomes and several CAPN inhibitors prevented it. Finally, in vivo inhibition of CAPN1 in 72-h-weaned mice decreased LAMP2a cleavage. Indeed, calpeptin-treated mice showed a substantial delay in tissue remodeling and involution of the mammary gland. These results suggest that CAPNs are responsible for mitochondrial and lysosomal membrane permeabilization, supporting the idea that lysosomal-mediated cell death is a new hallmark of mammary gland involution.

Total synthesis of iejimalide B

Iejimalide B, a structurally unique 24-membered polyene macrolide having a previously underutilized mode of anticancer activity, was synthesized according to a strategy employing Julia-Kocienski olefinations, a palladium-catalyzed Heck reaction, a palladium-catalyzed Marshall propargylation, a Keck-type esterification, and a palladium-catalyzed macrolide-forming, intramolecular Stille coupling of a highly complex cyclization substrate. The overall synthesis is efficient (19.5% overall yield for 15 linear steps) and allows for more practical scaled-up synthesis than previously reported strategies that differed in the order of assembly of key subunits and in the method of macrocyclization. The present synthesis paves the way for efficient preparation of analogues for drug development efforts.